This invention relates in general to programmable logic controllers and, more particularly, to a method for communicating among a plurality of programmable logic controllers.
In the past, a plurality of programmable logic controllers (PLC's) have been connected together by a common bus to enable communication among the controllers. For example, in FIG. 1, PLC's 10, 15 and 20 are coupled together via a common bus 25. Often in such configurations, one of the PLC's acts as a master device and the other PLC's act as slave devices. Typically in such arrangements, when the master device is communicating with a selected slave device, the remaining slave devices are held in a wait mode or are otherwise not performing processing in a maximally efficient manner since they generally must continually monitor bus 25 for instructions and message traffic.